Summary/Abstract Our prior work in HIV cohort studies provides insights into the viral, inflammation, immune activation and antiretroviral therapy related risk factors for HIV-related CVD risk. Yet, an understanding of its pathophysiology remains incomplete. Emerging evidence suggests that gut microbiota (GMB) altered during HIV infection correlates with increased immune activation and disrupted metabolite profiles, but the role of GMB in HIV- related CVD is unknown. Our preliminary data show that in HIV infection, progression of atherosclerosis is associated with higher circulating sCD14, a marker of monocyte activation, and increased tryptophan catabolism. This preliminary work presents two promising candidates linking GMB and CVD risk in HIV infection which we propose to study using integrated ?Omics? approaches. In addition to these hypothesis- driven study aims, we will also generate novel hypotheses linking GMB, host immune activation and metabolomics profiles associated with CVD risk. We will leverage the Women?s Interagency HIV Study (WIHS) and Multicenter AIDS Cohort Study (MACS) >20 year follow-up for biospecimens, atherosclerosis and other CVD measures, and HIV parameters. Our longitudinal semi-annual measures allow us to subset individuals according to long-term HIV treatment, disease progression markers (CD4+ T-cell count, viral load), and comorbidity, with inclusion of matched HIV-uninfected participants. In this project, We will extend our established collaborations with leading labs to gather multi-dimensional data among 400 women and men (~65% of whom are HIV+), including stool GMB metagenomics, serum and cellular inflammation and immunologic markers (sCD14, monocyte transcriptomics), metabolomics, and measures (carotid artery ultrasound imaging over 4 year follow-up). Findings from this intensively studied group will then be extended to a larger sample of 746 women and men with metabolomics and longitudinal atherosclerosis data. In this project, we will have the opportunity to identify immune activation and metabolites underlying the role of GMB in CVD, which may be specific to HIV+ individuals, or accentuated in the setting of HIV.